Overview

Testability in science is the capacity to independently verify whether a claim is true.

Importance to Science

Testability is the foundation for which all science operates. It's what allows science to build volumes of confirmed data in which to build models for scientific theories. Investigation proceeds in a fashion like this:

The scientist makes a claim as to how he/she thinks the phenomenon works.

The claim is constructed in such a way it can be tested.

The claim is tested.

At step 4, a conclusion is drawn for the claim; one of the following:

The claim is falsified

The claim was not validated

The claim was validated

The vast majority of all claims fall into category #2. Through falsification and testing, we can steer claims into the other two categories, and thus make progress. If all claims remained at "maybe, maybe not", we cannot accumulate any useful knowledge.

Relationship between Testability and Falsification

We couldn't falsify claims without testing, but we can test claims without the claims being falsifiable. Consider the example:

Russel claims that a homeopathic drug cures headaches. He gives a dose to a patient with a headache, and the headache dissipates.

While the claim appears to have passed, possibilities still remain open about other causes for the cure. The headache could have gone away on its own. The patient may have experienced the Placebo effect. Even if we were to repeat this experiment over and over, we'd never distinguish this possibility from the others. Through the addition of falsification, we can succeed at distinguishing.